Blender CUDA Rendering
I agree with @Matt, especially if you are on a laptop. Whether you are on a laptop or a desktop PC, I would check the following settings in Blender. Also, when using GPU rendering in Cycles, make sure to check the settings in the Properties tab -> Performance -> Tiles. By default the two numbers under the "Tiles" settings usually are 64 x 64 (pixels). If you are able to get your Nvidia GT 520 video card to work, try bumping up those numbers to 200 x 80 and see if that helps. The other thing i recommend checking is the "Sampling" menu in the Properties panel. If the final render has a high sample number (i.e. - 800 or above), that can also cause render time to be slow.